The present invention is directed to signal processing apparatuses, and especially to structures and methods for providing clock signaling for operating signal processing apparatuses.
Operation of many signal processing apparatuses, such as audio processing chips, involves responding to a system controller. There are occasions when the system controller effects shutting down or interrupting receipt of an external clock signal, sometimes referred to as a master clock signal. By way of example and not by way of limitation, in an audio processing chip used in connection with a compact disc (CD) player the master clock signal is shut down or interrupted when the player is not engaged in playing a CD, during initial powering up of the audio processing chip, when a user changes a CD or when an automatic CD changer changes a CD, when moving the reader head from track to track, and in other operational situations. There are times when the master clock is shut down or interrupted during which communications or other operations must be carried out, so there is a need for a clock signal for effecting those communications or other operations. Prior art signal processing apparatuses have addressed this need for continuing clock signaling by providing an external clock signal source, such as a crystal, for use when the master clock signal is shut down or interrupted.
In today's market the size of products, such as CD layers, is physically shrinking, and the profit margins of such devices are under pressure to be further reduced. In such market conditions, the addition of a crystal to a signal processing apparatus in a product amounts to adding too bulky and too expensive a component.
It would be useful to provide a source for a clocking signal for a signal processing apparatus when its master clock signal is shut down or interrupted that is less expensive and less bulky than a crystal.